1. Field of the Invention
The present invention relates generally to optical fiber devices and methods, and in particular to improved systems and techniques for generating Bessel beams.
2. Description of Prior Art
The class of spatial patterns of light called Bessel beams have attracted recent interest because of their propagation invariant, i.e., diffraction-free, nature. Unlike Gaussian beams, the central spot in Bessel beams do not expand with propagation in free space. In addition, Bessel beams can self-heal, i.e., completely re-form past an opaque obstruction. Thus, Bessel beams can navigate around dark objects, and are of immense interest in a variety of fields of science and technology. Their uses range from enhanced optical tweezers, microscopy, and perhaps even free-space communications and Light Detection and Ranging (LIDAR).
Creating these beam profiles has proven to be difficult for a number of reasons. One current approach involves the use of axicons, which are a special class of free-space lenses. However, since axicons are bulk, free-space elements, they require careful alignment, and are not useful in systems requiring remote delivery. Thus, a fiber-device approach for producing Bessel beams would be highly preferable for applications requiring stability and remote delivery.
In one attempt at a fiber-based solution, an axicon was machined onto a fiber tip. However, this device was unsatisfactory. In addition to being prohibitively expensive from a manufacturing standpoint, the resulting 2 μm beam from this device diverged in less than 40 μm, primarily due to the fiber's inherently small aperture. Thus, the device did not offer significant advantages over Gaussian beams.